Ceramically bonded refractory bodies used as linings in glass melting vessels should be capable of withstanding the severe environmental conditions created during furnace operations. Ideally, the linings of such vessels should be resistant to corrosion, erosion, provide thermal insulation and remain structurally stable over a wide range of temperatures for extended periods.
Refractory compositions based on zirconia, alumina and silica exhibit these characteristics to a great extent. However, such materials have not proved completely adequate in providing resistance to the alkaline vapors and dust present during glass melting. It has been observed that undesirable reactions occur between alkaline vapors, such as may be derived from sodium carbonate or sodium hydroxide, and zirconia-alumina-silica based brick. These deleterious reactions cause shelling, peeling, surface expansion of exposed bricks, contamination of glass batches and early structural failures of refractory linings, particularly in the upper sections of lined vessels where alkaline vapor condensates are formed.
Although bonded refractory compositions containing alumina, zirconia and silica have low apparent porosities, the prior art products undergo disintegration upon contact with the soda or potash vapors due to formation of expanded mineral phases composed of beta alumina and alkaline alumina silicate.
To overcome these disintegration features, the instant invention is directed to lowering the alumina content and to replacing most of the alumina with alumino-silicate materials which contain from 45% to 75% alumina.